Inductors and transformers are used in a wide variety of integrated circuit applications including radio frequency (RF) integrated circuit applications. An inductor is a passive electrical component that can store energy in a magnetic field created by the current passing through it. An inductor can be a conductor shaped as a coil or solenoid which includes one or more “turns.” The turns concentrate the magnetic field flux induced by current flowing through each turn of the conductor in an “inductive” area within the inductor turns. The number of turns and the size of the turns affect the inductance.
Two (or more) inductors which have coupled magnetic flux form a transformer. A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors, usually the coils or turns of the inductors that form the transformer. A varying current in a first or “primary” inductor induces a varying voltage in a second or “secondary” inductor. If a load is coupled to the secondary inductor, a current will flow in the secondary inductor and electrical energy will flow from the primary circuit through the transformer to the load.
Integrated circuits can be designed using different technologies, for example complementary metal oxide semiconductor (CMOS) technology, glass technology, sapphire technology, quartz technology, etc. These different technologies have different properties that make them better suited for different applications. For example, CMOS technology is well suited for active components, such as transistors, which can shrink as feature sizes shrink. However, passive components, such as inductors, do not shrink with feature size and can thus consume a relatively significant amount of space in CMOS technology. As another example, glass technology is not as well suited for active devices but, since it can be less expensive than CMOS technology, glass technology can be better suited for passive devices. There are various other properties that distinguish the various technologies which are known to those of skill in the art.
Conventional inductors implemented in integrated circuit dies and circuit packages can have several drawbacks. These inductors can be made by forming helical or spiral traces in conductive layers to form inductor turns. In some cases, these traces may be coupled to traces in adjacent layers in order to achieve higher inductance. Unfortunately, the inductors can consume excessive metal layer resources and may not provide sufficient current capacity or high enough quality factor without undesirable scaling. In addition, because the inductive areas of the inductors are substantially parallel with respect to other trace layers in the package substrate and circuit die, they can have unfavorable electromagnetic interference (EMI) effects on other components within the integrated circuit and/or their inductor characteristics can be adversely affected by adjacent conductors within the substrate or circuit die.
It would be desirable to have an inductor and transformer implementation that can create higher inductance values and yet take up less space desirable for other components and have less adverse EMI effects with other components.